1. Field of the Invention
The invention relates to a control device of an automatic transmission of a vehicle, and in particular to multiple shift control of the automatic transmission.
2. Description of the Related Art
In recent years, there is a trend toward more and more gear positions or speed ratios that can be established by a vehicular automatic transmission, and the intervals between adjacent upshift lines and downshift lines in a shift diagram used for determining a gear position to be established tend to be reduced with the increase in the number of gear position of the automatic transmission. Accordingly, the automatic transmission is more likely to be shifted up or down, as compared with conventional automatic transmissions, and a further shift determination (i.e., a determination that the automatic transmission should be shifted to a further higher or lower gear position) may be made during shifting of the automatic transmission. The term “multiple gearshift” is defined as a type of gearshift that is carried out when a further shift determination as described above is made during shifting of the automatic transmission.
In the multiple gearshift as described above, shift control is more complicated than that for a single gearshift, and therefore, shift shock is more likely to occur. In view of this situation, techniques for reducing shift shock during multiple shifting are disclosed in Japanese Patent Application Publication No. 2007-170638 (JP-A-2007-170638), Japanese Patent Application Publication No. 2001-27312 (JP-A-2001-27312), Japanese Patent Application Publication No. 11-63197 (JP-A-11-63197), and Japanese Patent Application Publication No. 10-281277 (JP-A-10-281277). For example, a control device of an automatic transmission as described in JP-A-2007-170638 inhibits switching of oil-pressure command values generated to friction devices of the automatic transmission so as to reduce shift shock, when a request for a further downshift (i.e., request for a multiple gearshift) is made due to an increase in the amount of depression of the accelerator pedal during a downshift.
In the meantime, when it is determined that an automatic transmission capable of establishing eight gear positions or eight speed ratios should be shifted down to the sixth gear position during downshifting from the eighth gear position to the seventh gear position, a multiple gearshift to the sixth gear position is started. In some cases, it is determined, depending on the amount of operation (or depression) of the accelerator pedal or the rate of change of the operation amount, for example, that the automatic transmission should be shifted from the eighth gear position directly to the sixth gear position without being shifted to the seventh gear position. Thus, when the automatic transmission is shifted from the eighth gear position to the sixth gear position, different shift controls are performed with respect to a multiple gearshift from the eighth gear position to the sixth gear position via the seventh gear position, and a single gearshift from the eighth gear position directly to the sixth gear position.
If it is determined that the automatic transmission should be shifted further down to the fifth gear position during shifting to the sixth gear position, it is difficult to start multiple shift control for an immediate gearshift to the fifth gear position, and multiple shift control for shifting to the fifth gear position is started when the automatic transmission is placed in a certain condition where the gearshift to the sixth gear position is substantially completed. At this time, it is desired to quickly shift the automatic transmission to the fifth gear position. However, when the gearshift to the sixth gear position is executed or started during shifting from the eighth gear position to the seventh gear position, in particular, a shift time it takes the transmission to establish the sixth gear position may be shortened due to an influence of the previous gearshift (i.e., gearshift from the eighth gear position to the seventh gear position), as compared with the case where the automatic transmission is shifted from the eighth gear position directly to the sixth gear position. Therefore, upon a multiple gearshift to the fifth gear position, a difference or deviation may arise between a command oil pressure of an engaging device and the actual oil pressure, and shift shock may occur if further shift control is exercised in this condition.